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Add the requirement for the probability sampler #570

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Add the requirement for the probability sampler #570

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Add the requirement for the probability sampler to include a span att…
Apr 20, 2020
e833c3c
Update specification/trace/sdk.md
jkwatson Apr 21, 2020
efb7376
shorten line lengths to 80
Apr 21, 2020
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4 changes: 4 additions & 0 deletions specification/trace/sdk.md
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Expand Up @@ -119,6 +119,10 @@ These are the default samplers implemented in the OpenTelemetry SDK:
that are root spans (no parent) and Spans with remote parent. However there
should be configuration to change this to "root spans only", or "all spans".
* Description MUST be `ProbabilitySampler{0.000100}`.
* If the probability is applied (as opposed to using the parent's
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It's surprising that this is a MUST since downstream tracers don't typically need to know the parent's sampling procedure, just its decision. This looks more like a SHOULD-level semantic convention to me.

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IMO, we want to have the Probability Sampler work the same everywhere. So, if we want to go forward with this change (and I'm relying on @pavolloffay for the justification/need), then I think that we should require them to all behave the same way. Hence, the use of MUST.

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@c24t this has no effect on downstream tracers, since the probability is merely recorded as span attribute, out of band.

`SampledFlag` value), the set of span Attributes returned in the result MUST
include an attribute with the key `sampling.probability` and a value of the
probability being used.
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sampling.probability would have the value that is calculated by the algorithm? It is not very clear what is value of the probability being used.

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I don't understand the concern. A probability-based sampler has a probability that it is configured to use. This is the sampling probability.


#### Probability Sampler algorithm

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